1. Field of the Invention
The present invention relates to a device and method which radiates a laser beam onto a workpiece to machine this workpiece.
2. Related Background Art
Conventionally, ink has been used when stamping the date of manufacture and a serial number on, for example, a can or the like. However, in a case where ink is used, there are problems regarding ink peeling and pollution of the environment. As a method of solving these problems, marking by laser machining is attracting attention. In the laser marking, fine holes are formed in a workpiece, such as a can, and alphanumeric characters or the like are stamped thereon by condensing and radiating a laser beam.
As machining methods for laser marking, both a method of forming dots one by one using one laser beam and a method of arranging an intensity mask on an extended laser beam to perform collective machining have been generally used in the past. However, in the former method, dots are formed one by one. Thus, there is a problem in that it is time-consuming. Additionally, in the latter method, the laser beam intercepted by the intensity mask did not contribute to the machining. Thus, there is a problem in that the quantity of light lost is large.
As a method of solving these problems, a method using a phase-modulation type spatial light modulator has started to be considered. That is, a hologram is displayed to the phase-modulation type spatial light modulator, a laser beam input to this spatial light modulator is phase-modulated for each pixel, the laser beam after that phase modulation is Fourier-transformed by a condensing optical system and imaged on a workpiece, and the workpiece is machined according to a machining pattern created by this imaging. A hologram according to a machining pattern in a workpiece is used as the hologram displayed to the spatial light modulator. This can reduce light loss and collectively form multi-points in a workpiece.
In the laser machining method using the phase-modulation type spatial light modulator in this way, first, the desired machining pattern in a workpiece is determined, calculation is performed on the basis of this machining pattern to create a hologram, this created hologram is transmitted to a driving unit of a spatial light modulator, the spatial light modulator is made to display the hologram by this driving unit, and a laser beam is then made to be incident on the spatial light modulator (refer to Japanese Patent No. 3475947).
Meanwhile, it is necessary to perform marking in real time on each of a number of workpieces which travel sequentially, for example, on a line. In a case where numeric values from “0001” to “1000” are marked on 1000 workpieces, respectively, as serial numbers, a series of procedures including machining pattern determination, hologram creation, and hologram transmission are repeatedly performed 1000 times when the above laser machining method is used.
However, in the above laser machining method, the time required for the series of procedures including machining pattern determination, hologram creation, and hologram transmission is long. Thus, in a case where marking is sequentially marked in real time on a number of workpieces respectively as described above, the throughput of laser machining is low.